The role of prostaglandin F2 alpha (PGF2 alpha) in luteolysis in the non-human primate is poorly understood. We have recently reported that chronic PGF2 alpha infusion to the corpus luteum via Alzet pump, induced premature, functional luteolysis in the rhesus monkey. In the present study we sought to determine the ovarian events leading to spontaneous luteolysis in the monkey. Rhesus monkeys underwent laparotomy during the early luteal (4-5 days after the preovulatory estradiol surge, PES), mid-luteal (7-9 days PES), and late luteal (10-14 days PES) phases or at the first day of menses (M). Concentrations of progesterone, estradiol, estrone, and 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) were measured in the ovarian venous effluents ipsilateral and contralateral to the ovary bearing the corpus luteum. Steroid levels in the ovarian vein on the corpus luteum side were significantly higher than the non-corpus luteum side throughout the cycle. PGFM levels were similar on both sides until the late luteal phase, when the effluent of the ovary bearing the corpus luteum contained significantly more PGFM (206 +/- 3) vs. 123 +/- 9 pg/ml, mean +/- sem); this disparity increased further at the time of menses (241 +/- 38 vs. 111 +/- 22 pg/ml). These data are the first to show an asymmetric secretion of PGFM in the ovarian venous effluent in the primate and suggest that PGF2 alpha of ovarian and possibly of corpus luteum origin may be directly involved in luteal demise.